The Identification of of Sub-centres in Two Italian Metropolitan Areas: a Functional Approach

This work introduces a method aimed at identifying metropolitan sub-centres based on an interaction approach, using commuting flows. In addition, it compares the results with other approaches based on employment and/or density thresholds commonly used in the literature. Although the scientific literature and the policy debate on polycentricity are increasingly devoted to its functional dimension, empirical research aimed at identifying metropolitan sub-centres mainly relies on employment density, which refers to a more morphological approach. After discussing the concept of centre and the contemporary literature on its empirical identification, the proposed methodology is applied to the metropolitan areas of Rome and Milan. Such a method shows a better fit compared to other approaches based on job density. Results are found to be remarkably sensitive to the method applied and are dependent, to some extent, on the different concept of centre that is adopted in the characterisation of metropolitan spatial structures.